SE468455B - QUADRATURE MODULATOR WITH MEDIUM TO COMPENSATE THE LOCALOSCILLATOR LEAK SIGNAL SUBJECT TO THE MODULE OUTPUT - Google Patents

Description

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GO -F> 10 15 20 25 30 35 (_51 2 since ie the local oscillator frequency is high and variable. The local oscillator signal leaked to the output signal causes a power peak in the point frequency, diode devices and even interferes with the reception of which causes disturbances in Due to this, the authorities have sometimes given provisions for a maximum level, the carrier component may have. as the leaked to the modulated signal. In addition, the transmission of the carrier consumes power unnecessarily, because it does not contain any information.

The problem related to the leakage of the local oscillator signal has previously been solved by striving to design the ones included in the modulator that they are good enough to use. However, in some cases this can be very difficult and expensive or even impossible. darna so, the frequency range. ligt. For example, it depends on the internal balance of the mixers 1 and 3 shown in Figure 1, how much the local oscillator signal LO leaks to the mixer output.

Efforts have further been made to correct this problem by summing the DC voltages which cause a constant component with local oscillator frequency in the output signal to two modulation signals I and Q. In the manufacturing or assembly phase of the modulator the DC voltages are manually placed so that the local oscillator frequency component of the output signal is of the same magnitude, but of opposite phase, as the local oscillator leakage signal of the modulator. signals each other.

In this case, these two obsolescence, rings and the possible replacement or change of the local oscillator generally increase, however, the local oscillator leakage generally increases when the modulator is in use.

Temperature change of the components- Intention. with the present invention, to provide an automatic adaptive control in a modulator operating according to the quadrature principle, which control eliminates this problem.

This object is achieved with a quadrature modulator of the type produced in the introduction, which according to the invention is characterized in that it comprises control means for regulating the magnitude of the compensation voltages independently of each other on the basis of the correlation between the output signal amplitude variation and the corresponding modulation signal.

The invention is based on the applicant's observation that the local oscillator leakage causes variation in the amplitude of the modulated output signal, which variation correlates with the modulation signals I and Q. This correlation is used in the invention to form voltages which compensate for the local oscillator leakage.

The solution according to the invention provides, as long as the modulation signals are present, to generate in the output signal of the modulator a suitable output component, which is of the same size, but of opposite phase, as the local oscillator leak signal of the modulator, to cancel the local oscillator leakage. The device works automatically and cancels the local oscillator leakage, which is caused by, among other things, the modulator's balancing error, heat creep and the frequency changes of the local oscillator signal.

The invention is advantageous to realize and with it one can considerably alleviate the requirements placed on the mixer of the modulator and the other components.

The invention will now be described in more detail by means of exemplary embodiments with reference to the accompanying drawing, in which Figure 1 shows a block diagram of a typical quadrature modulator and -l shows a block diagram of the modulator according to the invention with automatic compensation of the local oscillator signal leakage.

In the quadrature modulator in Figure 2, the actual modulator part is denoted by the reference numeral 15 and it may be, for example, of the type shown in Modulator part 15 comprising a local oscillator input LO IN and two modulation signal inputs.

An amplifier 14 is preferably connected to the output of the modulator 15, with which the modulated output signal is amplified to a power level, at which a power measuring circuit 13 connected to the output of the amplifier operates. The power measuring circuit 13 forms a feedback signal, such as a voltage which is proportional. From the feedback voltage, a direct current component is removed by means of a high-pass filter 12 connected to the output of the power measuring circuit 13 and its alternating current to the amplitude of the modulated output signal. component can preferably be amplified to a suitable level by means of an amplifier 5, series with a low-pass filter 12. The amplified signal connected in the loop is fed to one input of the correlator 6 and to one input of the correlator 9. To the second input of the correlator 6 a modulation signal I is applied and to the second input of the correlator 9 a second modulation signal Q is applied, the correlators comparing the feedback signal with the modulation signals I and Q. The output of the correlator 6 ie the correlation result is integrated over time with an integrator 7, so that from the correlation result the fast amplitude variations in the modulated output signal independent of the local oscillator signal leakage are removed. The compensation voltage 'generated in the integrator or filter 7 to the output of the summing means is supplied to one input of the summing means 8. In the second input, a modulation signal I is supplied, the summing means 8 summing the compensation voltage to the modulation signal, and in this case in its output generates a final modulation signal, which is supplied to the modulation input of the modulator 15. It depends on the polarity of the circuit solution and the previous block, whether the summing of the compensation voltage to the modulation signal really causes the compensation voltage to be added to the modulation signal or subtracted therefrom.

Correspondingly, an integrator or a low-pass filter 10 is connected to the output of the correlator 9 to remove rapid variations from the correlation results. The compensating voltage generated at the output of the correlator 10 is connected to one input of the summator means 11. A modulation signal Q is applied to the second input of the summing means 11, the summing means 11 forming a second modulation signal in the manner described above, which is fed to the modulator 15.

To the extent that the feedback signal formed by the power measuring circuit 13, the high-pass filter 12 and the amplifier 5 correlates, for example, with the modulation signal Q, there is a local oscillator signal component parallel to the Q modulation level, which is leaked via the modulator and strives to remove automatically by changing the magnitude of the compensating voltage supplied to the sum 11. The feedback of the I-lead works in a corresponding manner, insofar as the feedback signal correlates with the modulation signal I. In the quadrature modulator according to the invention, each compensation voltage is thus regulated independently of each other on the basis of the correlation between the corresponding modulation signal and the feedback signal.

From. the circuit solution shown in Figure 2 can »D- -F> (Ia 6 one remove either or both amplifiers 5 and 14, unless the output of the modulator is so strong that amplifiers are not needed.

The figures and the description relating thereto are intended only to illustrate the invention. Regarding the details, the present invention may vary within the scope of the appended claims.

Claims (5)

10 15 20 25 30 35 468 455 7 Patent claims Quadrature modulator with means (8, 11) for compensating the local oscillator leakage signal present in the output signal (RF OUT) of the modulator (15), which means sums different compensation voltages into two modulation signals (I, Q), characterized in that it comprises control means (6, 9, 13) for regulating the magnitude of the compensation voltages independently of each other on the basis of the correlation between the amplitude variation of the output signal (RF OUT) and the corresponding modulation signal (I or Q). Quadrature modulator according to claim 1, characterized in that it comprises a detector means (13) connected to the output of the modulator (15) for forming a feedback signal which is proportional to the amplitude variations of the output signal (RF OUT), two correlator means (6, 9), of which to one (6) inputs a feedback signal and a first modulation signal (I) are connected to form a first compensation voltage and of which to the other (9) input a feedback signal and a second modulation signal (Q) are connected to form a second compensating voltage, and a first (8) and a second (11) summing means for summing the first compensating voltage to the first modulating signal (I) and for summing the second the compensation voltage to the second modulation signal (Q). 3. A quadrature modulator according to claim 2, characterized in that the compensation voltages are connected to the summator means (8, 11) via integrators or low-pass filters (7, 10). 4. A quadrature modulator according to claim 2, 8 or 3, characterized in that the output of the modulator has an amplifier (14) before the detector means (13). Quadrature modulator according to Claim 2, 3 or 4, characterized in that the low-pass filter (12) and the amplifier (5) are connected in series between the inputs of the detector means (13) (6, 8). hence, output and correlants' IM